The Dr. Ph. Martin's Iridescent Colors flow off a pen tip smoothly and evenly giving an extended writing distance. -toxic, and conform with ASTM D4236.The colors will flow through an airbrush effortlessly, and are also excellent for Illustration, Designing, and Rubber Stamping.Sold in 1 oz. bottles with the highly preferred dropper top for controlled application. Al l colors are intermixable with each other.